Process for the preparation of low contact resistant contact on a high transition temperature superconductors

Abstract

Disclosed is a three layer process for making contact points to a high transition temperature superconductor (HTSC), particularly to (Bi,Pb) 2 Sr 2 Ca 2 CU 3 0 19+x with and without silver in the superconductor. The contact structure is a three layer configuration with a perforated silver foil ( 3 ) sandwiched between two metal spray gun deposited silver layers ( 2,5 ) and subsequent heat treatment in air. The contact has been made on tubes and rods ( 1 ). The silver contacts are capable of carrying a continuous current of 200 Amps without adding any substantial heat load to the cryogen used to cool the HTSC. The contact resistance at 4.2 K is in the range of 1.5×10 (hoch −8) to 8.5″ 10 (hoch −8) OHM in zero applied filed.

1. A contact made by a process comprising the steps of: making a groove at the end of a superconductor, depositing a first silver layer by metal spray gun at a temperature of 120° C., heating the deposited silver layer at a temperature in a range of 200-250° C. for a time period in the range of 2-5 hrs, wrapping a perforated silver foil on the heat treated first silver layer, depositing a second silver layer by metal spray gun at a temperature of 120° C., heating the combination of first silver layer, wrapped perforated silver foil and second silver layer at a temperature in a range of 830-850° C. in air for a time period in the range of 100-150 hrs, wherein contact resistance is in a range of 3.07×10 −6  to 3.0×10 −7 Ω in zero applied magnetic field at 77K. 
     
     
       2. A contact made by a process comprising the steps of making a groove at the end of a superconductor, depositing a first silver layer by metal spray gun at a temperature of 120° C., heating the deposited silver layer at a temperature in a range of 200-250° C. for a time period in the range of 2-5 hrs, wrapping a perforated silver foil on the heat treated first silver layer, depositing a second silver layer by metal spray gun at a temperature of 120° C., heating the combination of first silver layer, wrapped perforated silver foil and second silver layer at a temperature in a range of 830-850° C. in air for a time period in the range of 100-150 hrs, wherein the contact resistance is in a range of 1.5×10 −8  to 8.5×10 −8 Ω in zero applied magnetic field at 4.2K.